Tough, Self-Adhesive, Antibacterial, and Recyclable Supramolecular Double Network Flexible Hydrogel Sensor Based on PVA/Chitosan/Cyclodextrin

Hydrogel-based flexible sensors have attracted extensive attention of researchers due to their great application potential in soft robots, electronic skin, motion monitoring, and disease diagnosis. However, it is still a challenge for hydrogel-based flexible sensors to be integrated with good mechanical performance, sensitivity, self-adhesion, fatigue resistance, antibacterial activity, and recyclability. Here, a novel supramolecular polyoxymethylene cross-linking agent (PCD-Fc-CHO) was designed and synthesized by the host–guest interaction between poly(β-cyclodextrin) and ferrocene. Then, a double network (DN) hydrogel was prepared by a PVA crystallization domain via the freeze-thaw cycle method (first network) and Schiff base between PCD-Fc-CHO and chitosan (second network). The obtained DN hydrogel was immersed in the NaCl solution to form a conductive DN hydrogel. The resulting hydrogel has excellent mechanical properties [tensile (314%, 0.5 MPa), compress (50%, 0.663 MPa)], good fatigue resistance (stretching and compressing cycles at least five times), reliable conductivity (2.48 S/m), high sensitivity [gauge factor (GF) = 4.87], antibacterial, and recyclable properties. In addition, an industrially produced and low-cost plant polyphenol, black wattle tannin, was used for the first time to give the hydrogel good adhesion and repeated adhesion (at least ten times). The obtained hydrogel can be used as a flexible strain sensor to monitor both large movements (bending finger, wrist, elbow, arm, and knee) and micromovements (talking, smiling, blinking, blowing, frowning, and drinking) with high sensitivity and stability. It is noteworthy that the reshaped hydrogel also exhibits sensitive sensing performance, indicating that the hydrogel can be recycled. This work expanded the strategy for the design and preparation of multi-functional DN hydrogels and promoted the application of wearable, highly sensitive, fatigue resistance, antibacterial, and green hydrogel sensors.